A data storage device, such as SSD (Solid State Drive), SD (Secure Digital) memory card or portable flash memory, is mainly constituted of a control unit and a data storage medium. The data storage medium is constituted of a plurality of data columns for storing data.
Inevitably, secondary products may be produced in the manufacturing process of data storage devices. Therefore, it is necessary to screen out all bad columns in the data storage medium and label or record the bad columns in a bad column table before releasing the secondary products to the market. According to the bad column table, the control unit is blocked from accessing the labeled bad columns so as to avoid data access error during operation.
Conventionally, the number of available labels (or records) for bad columns is limited (for example, a total of 254 labels at most). Therefore, if the data storage medium is largely defective and the available labels for bad columns are used up, some storage areas in the data storage medium having normal and valid columns would be labeled as bad storage areas as the correcting capability (e.g., 44-bit correction) of the ECC (Error Correcting Code) has been exceeded. Thus, the normal and valid data storage space is wasted and the valid capacity in the data storage medium is reduced.